The new iOS 9.1 beta, build 13B137 (13B5137 for public testers), is available as an over-the-air update and through Apple’s Developer Center. There’s a second build, 13B139 (13B5139 for public testers), that’s unique to the newly released iPhone 6s and 6s Plus. The latest beta seems to just offer security and performance improvements to the overall system.
The new version of iOS will make improvements to the overall system performance and security alongside introduce support for Unicode 8 and new emojis such as a taco, burrito, cheese wedge, middle finger, unicorn head, and more. You also have the option to hide your contact’s set photos in Messages in the new software.
It is assumed that the public version of iOS 9.1 will be released alongside the new iPad Pro and Apple TV 4, due to the software update containing support for the iPad Pro’s accessories and tools for setting up the Apple TV 4 through an iOS device.